This article discusses some characteristics of opposition movements in Leninist regimes. The first part develops the concept of Leninist regime. Linking assumptions of totalitarianism and modernization theory, I point at the fundamental dilemma of Leninism as a political form of modern society: the maintenance of charismatic self-definition and monocratic control in an increasingly differentiated and pluralistic society. The second part explicates the meaning of opposition in Leninist regimes, and develops a typology of opposition movements (revisionism, dissidence, nationalism). The purpose of this analysis is to clarify the logic of social movements in Leninist regimes, and it may be considered a prolegomenon to further empirical work.